1. Field of the Invention
The present invention relates to a displacement information detection apparatus, a displacement information detection scale, and a drive control apparatus using the apparatus. The present invention can be particularly suitabe for a rotary encoder for detecting a rotation position, a rotation position deviation amount, a rotation position deviation direction, a rotational speed, the rotational acceleration, and the like, by irradiating a light beam onto a radial diffraction grating and a code pattern on a disk attached to a relative rotary object, and detecting modulated signal light obtained therefrom, and an apparatus (e.g., a motor with an encoder) for attaining rotational movement of the object by controlling the current amount and direction of a driving apparatus such as an AC motor or the like on the basis of the detection information.
2. Related Background Art
Conventionally, an incremental rotary encoder is utilized for the purpose of measuring the rotation information (rotation displacement amount, speed, acceleration, and the like) of an object with high precision. On the other hand, a brushless motor represented by an AC motor utilizes an absolute rotary encoder for detecting the absolute rotation position of a rotor in the motor so as to perform rotation.
For this reason, in rotation position control of an object utilizing an AC motor or the like, a composite type rotary encoder which can obtain both types of signals is used.
In a high-precision incremental encoder, a monochrome light beam is irradiated onto a scale on which a very fine grating pattern on the micron order is recorded, and at least two diffracted light components obtained by this scale are extracted and interfered with each other, thereby generating a periodic change in amount of light upon movement of the grating. A photoelectric conversion element detects this change to output an incremental encoder signal.
An absolute rotary encoder outputs the absolute rotation position of a disk by detecting transmitted light (or reflected light) at a specific position on each circumference when a plurality of transmission/non-transmission (or reflection/non-reflection) patterns (e.g., gray code patterns) are formed on circumferences at different radial positions on the rotary disk so that only a specific combination of codes is detected per revolution.
An absolute encoder for a motor outputs the relative position between the rotor and stator of the motor by detecting transmitted light (or reflected light) at a specific position on each circumference when a plurality of transmission/non-transmission (or reflection/non-reflection) patterns (e.g., gray code patterns) are formed on circumferences at different radial positions on the rotary disk so that only M combinations of codes are available in correspondence with the motor structure (the number M of poles).
The recent trend is to require a size reduction (e.g., a disk with a diameter of 10 mm) of encoders. However, it is difficult to attain such size reduction of a composite encoder based on the different principles, as described above.
Optical systems based on the different detection principles may be simply juxtaposed, and size reductions of the respective optical systems may be separately attained. In this case, a size reduction attained by the overall structure is limited. In particular, when a plurality of patterns for the composite encoder are formed on a scale, patterns capable of attaining both a compact structure and high-precision detection are required.